(1) Field of Invention
The present invention relates to a colored polymer emulsion having a film-forming property at normal temperatures, and to the process for the preparation of the colored polymer emulsion.
This colored polymer emulsion is valuable as a base material of an aqueous ink and can be widely used as a coloring material for paper, fibers, and wooden articles.
(2) Description of the Related Art
Inorganic and organic pigments have been used for the coloration of an aqueous polymer emulsion. Furthermore, an aqueous solution of an acid dye or direct dye has been used as a coloring material.
However, coloration with pigments is unsatisfactory in that the kinds of colors obtainable from pigments are limited, it is impossible to obtain the desired high color density, and pigments are generally expensive. Moreover, to attain the intended coloring effect of pigments in an aqueous ink, before application of the pigments, it is necessary to pulverize the pigments by various means and disperse the resulting fine particles in water by using a large amount of a dispersant or dispersion stabilizer.
In the conventional method for coloring a polymer emulsion with a pigment dispersion as mentioned above, the polymer emulsion acts as a binder for the water-insoluble pigment particles and the polymer per se in the polymer emulsion is not colored.
Where an aqueous solution of an acid dye or direct dye is used as a colorant, since the colorant is water-soluble, the water resistance of the coloring material after drying is extremely poor, and bleeding of the color is caused by immersion in water or sweating, or sometimes color wash-out occurs. Also, in this case, the polymer in the polymer emulsion is not colored.
As means for overcoming these disadvantages, a proposal has been made in which colored particles of an acrylonitrile type polymer are used as the colorant for an aqueous polymer emulsion (see Japanese Unexamined Patent Publication No. 52-80340).
In this proposed method, in order to obtain a finely divided polymer such that colored polymer particles can be used as the colorant, it is necessary to adopt a very special polymerization process (for example, the polymerization is carried out at a temperature of at least 120.degree. C. under a high pressure of 5 to 50 atmospheres). Moreover, the composition of monomers constituting the polymer particles is extremely limited and the polymer particles cannot be used in the field where a film-forming property or softness is required.